The present invention relates to a connecting structure for connecting slider pads and lead pads with each other through solder balls in a head gimbal assembly used in a magnetic disk drive. More specifically, the present invention relates to a solder ball connecting structure suitable for the re-utilization of a suspension assembly.
Recently, magnetic disk drives have come to be used in various electronic devices and the necessity of improving the yield in mass production has become more and more important than before. The magnetic disk drive incorporates a head gimbal assembly (hereinafter referred to as “HGA”) which supports a slider formed with a magnetic head for reading and writing data. The HGA includes a head/slider having a magnetic head and a slider, a flexure which permits the head/slider to fly above a magnetic disk and perform a track following operation while performing a soft pivot motion, a load beam for applying a preload force to the flexure, a mounting plate for fixing the load beam to an actuator assembly, and a lead wire for connecting the magnetic head and a circuit board with each other. The construction of the HGA exclusive of the head/slider is designated a suspension assembly.
The head/slider is formed with a slider pad which plays the role of a relay terminal for connecting the magnetic head to a lead pad formed at an end of the lead. The head/slider is fixed to a flexure tongue of the flexure with an adhesive after formation of the suspension assembly. After fixing the head/slider to the flexure tongue, it is necessary to connect the lead pad and the slider pad electrically with each other.
The connection surfaces of the lead pad and the slider pad are placed in a positional relation such that planes including those connection surfaces intersect each other perpendicularly (a virtual right angle is formed at an intersecting point of both pads' connection surfaces when seen sideways). Examples of a technique for connecting both pads include a solder ball connecting method described in Patent Document 1 (Japanese Patent Laid-Open No. 2003-123217). According to the solder ball connecting method, first the HGA is supported in such a manner that a virtual right angle formed by both pads faces vertically upward, and the solder ball is disposed so as to contact both pads. Thereafter, a laser beam is applied to the solder ball to melt the solder, thereby connecting both pads.
FIG. 11 shows a lead pad-slider pad connecting structure described in FIG. 6 of Patent Document 1. A flexure 101 in a suspension assembly is of a two-layer structure comprising a polyimide layer 102 which is an insulating polymer material and a stainless steel foil layer 103. Lead wires 104 are formed by a conductor layer on the polyimide layer 102 and lead pads 105, which are wider than the lead wires 104 so as to have an area sufficient for solder ball connection, are formed at ends of the lead wires 104.
The polyimide layer 102 and the stainless steel foil layer 103 can be processed into predetermined shapes by covering required portions with resist and subsequent etching. In the case where the polyimide layer 102 is a photosensitive polyimide layer, the photosensitive polyimide layer 102 can be processed into a predetermined shape by covering required portions of the photosensitive polyimide layer with resist and subsequent exposure and development. An aperture 106 is formed in a front end portion of each lead pad 105 in the flexure 101 in order to avoid adhering of protruded adhesion to the lead pad 105 at the time of bonding a head/slider 108 to the flexure 101 or in order to avoid a change of the polyimide layer 102 as a polymer material due to the generation of heat under the application of a laser beam.
Therefore, the front end portion of each lead pad 105 is formed as an aerial wiring projecting into the aperture 106. In each lead pad 105 is formed a concave portion 110 in a symmetric shape with respect to a center line CL of the surface of the lead pad. Slider pads 109 of the head/slider 108 are arranged at positions perpendicularly intersecting the lead pads 105 as noted earlier. Therefore, virtual orthogonal axes defined by a plane extending from a connection surface of each slider pad 109 and a plane extending from a connection surface of the corresponding lead pad 105 intersect each other are at an angle of 90° (right angle). In case of connecting each slide pad 109 and the corresponding lead pad 105 with each other by use of a spherical solder ball 200, the HGA is fixed in a direction in which a virtual right angle defined by each slider pad 109 and the corresponding lead pad 105 for temporarily fixing the solder ball 200 faces vertically upward and is open.
Usually, the HGA is fixed in such a manner that each lead pad 105 on the flexure 101 and the corresponding slider pad 109 on the head/slider 109 are each at a rising angle of 45° from a horizontal plane while maintaining the mutual orthogonal positional relation. When the solder ball 200 is dropped by gravity into the concave portion 110 of each lead pad 105 from a solder ball transfer device (not shown), the solder ball is held by both pads at the position of the center line CL. Thereafter, the solder ball 200 is heat-melted by means of a laser beam irradiator (not shown) to connect both pads. For improving the quality of the solder ball connection it is necessary to position the solder ball 200 on the center lines CL of both pads and thereafter apply a laser beam to the solder ball to melt the solder. In this case, the concave portion 110 can prevent the solder ball 200 from rolling on the surface of the lead pad 105 and deviating from the center line CL.
After connecting the lead pads and the slider pads with each other through solder balls and before incorporation into a magnetic disk drive, the HGA is subjected as a single member to a function test under the application of an electric signal. The magnetic head is a particularly delicate component among the components of the magnetic disk drive and may be at fault from the beginning or may become inoperative during assembly of the HGA due to the discharge of static electricity or an external shock. As a result, the HGA does not pass the function test in some cases. Most of the causes of failure of the HGA in the function test are attributable to the magnetic head. Therefore, if the head/slider alone can be removed from the HGA and replaced with another one, permitting re-utilization of the suspension assembly, then the improvement in yield of the HGA and the reduction of manufacturing cost will conveniently be achieved.
In the solder ball connecting structure of FIG. 11 described in Patent Document 1, however, when the solder which has been solidified to connect the lead pads and the slider pads with each other is removed and the head/slider 108 is dismounted from the suspension assembly, the solder remains within the concave portion 110 of each lead pad. Since the lead pads are fragile in structure, it is difficult to remove the solder from each concave portion 110 so as to permit re-utilization of the suspension assembly. In particular, since a high melting lead-free solder has often been used recently, it is becoming more and more difficult to remove the solder remaining in the concave portion 110. This is because the lead wires and polyimide layer may be damaged if still higher thermal energy is applied to the lead pads for melting the lead-free solder.
In the suspension assembly with solder remaining with each concave portion 110, the solder ball 200 cannot temporarily be fixed at the position of the center line CL at the time of replacing the head/slider and making re-connection through solder balls, so that it is impossible to effect solder connection of good quality.